Quartz crystal



FIG. 1 is a perspective view of the front, bottom and left side of quartz crystal showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a right side view thereof.

The elements shown in broken lines are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for quartz crystal, as shown and described. 